Sandel, who studied Limestone County's sunfish population from 2006 to 2010 while pursuing a doctoral degree in biology, said the area proposed as critical habitat was unlikely to ever be developed because it is too swampy. The three families that own most of the land along Beaverdam Creek - the Sewells, Hortons and McDonalds - previously signed voluntary conservation easements with the Fish & Wildlife Service promising not to disturb the most sensitive spots.

"I think it's going to be a thriving community with businesses and schools and homes," Sandel told AL.com in a Thursday phone interview. "We just need to be careful about how many people are drilling wells in the watershed, because that can cause the stream to dry up."

Sandel, a postdoctoral research fellow in statistical genetics at the University of Alabama at Birmingham, said another concern is a large City of Huntsville sewer line on the east side of Beaverdam Creek. The line is less than 50 feet from the creek at its closest point, he said.

"There's a real risk for contamination" if the line were to break, said Sandel.

Beaverdam Creek, which starts as an underground spring east of Powell Road and flows south for eight miles to the backwaters of the Tennessee River, is the last place on Earth where the spring pygmy sunfish is known to exist. Sandel estimates the population at "over 5,000."

Shane Davis, Huntsville's director of urban development, said converting the farm fields around the creek into subdivisions could be good for the long-term health of the spring pygmy sunfish. Tilled farm soils that now get washed into the creek will eventually become lawns that trap rainwater, he said.

"We're a nature-friendly community," Davis said Wednesday. "We want to protect the habitat, but we also want it to be reasonable."

Davis said the sunfish's new status as a threatened species will not affect plans to turn the 1,322-acre Sewell farm off Powell Road into a TVA Megasite for industrial development. The proposed Megasite is about half a mile west of Beaverdam Creek and sits entirely outside the proposed critical habitat, he said.

Huntsville is paying the Sewell family $300,000 a year to keep the land under option through late 2015.

The city, Limestone County and Alabama Department of Commerce are "actively marketing" the property to potential manufacturers for $20,000 an acre, said Davis.

Sandel and the Center for Biological Diversity petitioned the Fish & Wildlife Service in 2011 to protect the spring pygmy sunfish under the Endangered Species Act. In a news release this week, the center said the fish is threatened by "urban sprawl from metropolitan Huntsville, poor agricultural practices and loss of streamside vegetation."

"Hundreds of freshwater species in Alabama and the Southeast are staring extinction in the face," said Noah Greenwald, the center's endangered species program director.

"Without help, we risk losing species like the spring pygmy sunfish forever."